Elongated objects such as wires, rods and tubular or flat shapes (such as tubing, strip, plates, etc.) are oftentimes contaminated with undesirable surface coatings. In the case of steel wires, manufacturing often results in the formation on their surface of oxides, including rust or impurities such as dirt particles, lubricant and compound residues, etcetera.
In the case of copper wires, exposure to the environment results in copper oxidation in the form of a surface scale which consists of a mixture of cuprous (red) and cupric (black) oxides. Such oxidation layer needs to be removed from the copper surface because it greatly reduces the strength of the copper wire and its ability to withstand further processing.
There have been a number of techniques suggested by the prior art to remove surface contamination. For example, U.S. Pat. No. 1,993,400 teaches various methods for annealing and oxidizing a wire to remove known and unknown soap or grease compounds used in drawing the wire to size, by passing electric current through the wire to heat it. The book entitled "Ferrous Wire", vol. 1, chapter 6--Chemical Cleaning and Coating, published by the Wire Association International Inc., discloses various methods to clean ferrous wires, such as pickling, ultrasonic cleaning, etcetera. Batch pickling still remains the most commonly used cleaning method in the wire industry to remove surface contaminants. In this method, baths of either sulfuric or hydrochloric acid are placed in line in such a manner that the material may be dipped in acid tanks, rinse tanks, lime, borax and finally baked before passing the metal onto the wire mill itself.
Although it has been suggested, e.g., in U.S. Pat. No. 4,401,479, that ultrasonic cleaning can be employed to remove surface contaminants, apart from specialized one-wire systems, ultrasonic cleaning in standard tanks is seldom used for wire, since the energy concentration is usually too low for one-pass continuous-line systems.
Flash pickling is also disclosed in this patent. However, flash pickling unfortunately produces fumes and strong acid carryover. As a result, hazardous and environmentally damaging effluents are an important concern for this type of industry. The earliest treatment for effluents was to direct the spent acids to a nearby stream resulting in acid pollution, aeration and the precipitation of offensive metal salts. Large quantities of acids and alkalis cannot obviously be disposed of because of their influence on the environment. Treatment in some fashion, therefore, becomes necessary. Most countries have laws precluding stream pollution by acids, alkalis and metals. To cope with this situation, a number of alternative schemes have been proposed such as ponding, deep well disposal, neutralization with alkali, ammonia or slag, sulfuric acid recovery by cooling saturated solutions and hydrochloric acid recovery by roasting. None of these approaches completely address the environmental hazards. In addition, sophisticated solutions are costly.
U.S. Pat. No. 4,064,884 discloses a method and device to clean the surface of, e.g., a wire, by washing said surface with a washing liquid which is substantially the same kind as the one used in the last surface treatment step of said surface. U.S. Pat. No. 4,401,479 discloses a process of ultrasonic cleaning in a liquid to clean the surface of a wire and catalyze the rusting chemical reactions in order to use the wire in a concrete structure. U.S. Pat. No. 4,713,153 discloses a process and apparatus for cleaning by electrochemical pickling. U.S. Pat. No. 4,754,803 also discloses chemical pickling of copper rods. U.S. Pat. No. 4,899,798 discloses the recovery and the reuse of organic pickling vapors in copper bar and rod manufacture. U.S. Pat. No. 4,944,808 discloses a method to remove particles from a flexible support, much as a flexible sheet. European Patent 474,345 discloses a method to remove particulate matters from articles by the use of a liquid cryogen in which the articles are totally immersed in the liquid cryogen. As the articles are supported while immersed, the particles fall at the bottom of the cryogenic liquid bath, and the articles are further removed.